Many disorders in mammals and other living bodies are due to the lack of proper functioning natural cells of one type or another, with consequent lack of essential substances normally secreted by such cells. For example, diabetes is a disorder resulting from lack of properly functioning pancreatic islet cells, which normally produce and secrete insulin in response to glucose. Attempts to alleviate such conditions by transplantations of living, functioning animal cells, e.g. pancreatic islets, are limited by the immune rejection of these cells by the host body. Although the immune system can be artificially suppressed through chemotherapy and the transplant given an opportunity to succeed, this approach is not practical for large scale transplantations. The benefit to diabetics of such a pancreatic islet transplant would be enormous since not only would their reliance on exogenous insulin be reduced, but the insulin would be delivered in the natural control mode avoiding the periodic variation in glucose level associated with conventional therapy. It is believed that these variations are responsible for the degenerative complications of diabetes.